The present invention relates to an off-premises signal transmission device for distributing cable television ("CATV") signals to a plurality of CATV subscribers.
In a conventional CATV system, CATV signals are transmitted by a CATV cable from a head end to a plurality of subscribers located remotely from the head end. The cable system includes one or more trunk cables extending from the head end, a plurality of feeder cables branched from the trunk cable, and a plurality of drop cables branched from the feeder cables for delivering the CATV signal to subscriber homes. Each subscriber has one or more in-home CATV converter/tuners connected to the drop cable entering the subscriber's home. The CATV converter/tuner enables the subscriber to select one of a plurality of CATV signals (channels) available on the drop cable. The CATV service company enables the in-home CATV converter to allow the subscriber to view those TV channels to which he or she has subscribed.
There are at least two problems associated with the above-described conventional CATV system. First, the subscriber has access to the in-home converter and may modify that device to receive TV channels for which he has not subscribed, thus resulting in a loss of revenue to the CATV service company. Second, the subscriber may remove the expensive CATV converter, e.g., in the event that the subscriber moves. Again, the CATV company incurs a loss.
To solve these problems, it is possible to design a CATV system in which the expensive converter/tuner and other electronic circuitry is located in an external control unit or signal transmission device attached to and in series with a feeder cable. The external control units are typically mounted outdoors, e.g., on or adjacent to utility poles. Each external control unit includes a plurality of converter/tuners for providing cable TV signals to a plurality of subscribers via drop cables connecting the external control unit to each subscriber's house. Each subscriber has a subscriber processing unit which can communicate with the external control unit via the drop cable to allow the subscriber, using keys on the subscriber processing unit, to request a TV channel for viewing.
A requirement for a CATV system having external control units as above-described is to improve maintenance efficiency and to minimize as much as possible the disruption of cable TV service to subscribers in the event of the need to repair an external control unit. It is known that signal transmission devices connected in series with a CATV cable, such as tap-off devices, can be arranged as shown in FIG. 1. Reference numeral 11 is a box-like main housing. Cover 12 is supported on main housing 11 such that the cover can be freely opened and closed with respect to the main housing. A recessed chassis 13 is disposed in main housing 11. Collars 131 and 132, respectively having input and output connecting terminals 14 and 15, are formed at two ends of chassis 13. Input and output connecting terminals 14 and 15 are connected to feeder cable 16 to which a plurality of other tap-off devices are connected at various locations along the cable. Input and output connecting terminals 14 and 15 are coupled to each other through a connecting cable 17 disposed along the rear surface of chassis 13, as shown in FIGS. 2(a) and 2(b). Internal electronic units 18 connected to input connecting terminal 14 are arranged on chassis 13.
In signal transmission devices having the configuration described above, when one of internal units 18 (FIGS. 2(a) and 2(b) is broken or must be replaced with a new one, repair or replacement can only be performed after feeder cable 16 is removed, since not only internal units 18 but also input and output connecting terminals 14 and 15 are mounted on chassis 13. In such a case, CATV signals cannot appear at the output feeder cable 16, and thus CATV signals cannot be further transmitted along the feeder cable to subsequent subscribers down the line.
In order to solve the above problem, the input feeder cable 16 must be connected to output feeder cable 16 through a short-circuiting pin or wire (not shown) at the time of repair or replacement of the defective internal unit 18. This results in a time-consuming and cumbersome operation. The present invention has been made in consideration of the above situation, and has for its object to provide a signal transmission device which allows maintenance and repair procedures to be performed on CATV external control units while minimally disrupting the transmission of CATV signals to subscribers further down the cable.